Numerical design study on a high-powered segmented-type arc plasma torch for a high-enthalpy supersonic plasma wind tunnel

摘要

As a high-powered plasma source to produce a specific enthalpy higher than 20 MJ/kg at an air flow rate of 50 g/s for a supersonic plasma wind tunnel, a segmented-type arc plasma torch with an input power level of MW class is characterized in this paper. For this purpose, a numerical parametric study was carried out to determine the main design parameters, such as, the constrictor length L_C, the diameter of segmented disk D_C, and the diameter of the electrode D_E, under the requirements of specific enthalpy and air flow rate. From the results of the numerical study, firstly the plasma power and specific enthalpy are found to increase with increasing L_C at the expense of the torch efficiency, which is defined as the ratio of the total exit enthalpy to the plasma power. On the other hand, an increase in D_C is observed to improve the torch efficiency by reducing the plasma power at a fixed arc current and gas flow rate. Moreover, an increase in D_E is also found to contribute to improvements in the torch efficiency and the specific enthalpy by expanding the high-temperature region of the arc plasma and decreasing plasma velocities at the torch exit. Accordingly, a scale up to MW class for obtaining a high specific enthalpy can be achieved efficiently by inserting segmented disks with relatively large diameters between enlarged electrodes and then increasing the arc currents. For example, if the length of a constrictor consisting of segmented disks with a diameter of D_C = 25 mm is extended to L_C = 900 mm and then the arc current is increased up to 800 A, it is predicted that a specific enthalpy of 21. 2 MJ/kg can be achieved at a plasma power of 2. 89 MW and an air flow rate of 50 g/s, which corresponds to a torch efficiency of 36. 6%. Based on these numerical parametric study results, we expect that a segmented arc plasma torch can be designed to meet the requirements of a supersonic plasma wind tunnel, such as a specific enthalpy, air flow rate and plasma power.